Inductance arrangement

ABSTRACT

An inductance arrangement is directed to inductors, chokes and transformers with a very high power density. Chokes comprise a magnetic circuit and an electrical circuit, the latter usually comprising a copper winding. The inductance arrangement improves cooling of the magnetic circuit, efficiency of the induction arrangement, and reduces the consumption of material for the windings for a lower weight and a reduced structural size. Individual plate packs in the induction arrangement are displaced relative to each other to increase the surface area at both sides of the iron core. Displacement of the plates of the limbs allows for effective cooling passages or ducts between the core and the surrounding winding.

The invention concerns an inductance arrangement or the construction ofinductors, chokes and transformers with a very high power density.

Chokes are usual examples of inductance arrangements. Such a chokecomprises a magnetic circuit and an electrical circuit, the latterusually comprising a copper winding. Depending on the respective area ofuse involved the magnetic circuit comprises laminated dynamo plates atlower and medium frequencies, while at higher frequencies it comprisesfor example ferrite.

Such a choke usually comprises two magnetically conductive limbs whichare each enclosed by a respective copper winding and which aremagnetically coupled together by yokes, wherein depending on therespective situation of use involved an air gap can be provided betweena limb and a yoke. In this respect the inductance of such a choke can becalculated as follows:

(Equation 1) $L = {\frac{A_{Fe}}{I_{Fe}}\mu_{0}\mu_{e}N^{2}}$

wherein: A_(Fe) denotes the iron cross-section, I_(Fe) denotes thelength of the iron path, N denotes the number of turns, μ₀ denotesrelative permeability and μ_(e) denotes effective permeability.

Magnetic induction accordingly can be calculated in accordance with thefollowing formula: $B = {\frac{N \cdot I}{I_{Fe}}\mu_{0}\mu_{e}}$

Magnetic induction is the determining factor in regard to the design ofinductive components or transformers. An increase in inductance of theinduction B always also means a higher power density.

The iron losses P_(V,Fe) within the magnetic circuit (core) aredependent in a wide range at low frequency in quadratic relationship onthe inductance B. This is shown in FIG. 2. With even greater driving ofthe dynamo plate the iron losses rise very steeply, for which reasonthat range should generally be avoided. Conventional types of chokeshowever do not entail the possibility of dissipating high power lossesas the iron limbs are insulated from the ambient atmosphere by the coilbody, that is to say the copper winding. In this case there ispractically no possible way of heat dissipation by radiation (windingover core) or heat dissipation by conduction (air gap). Therefore only asmall amount of power loss can be removed from the magnetic circuit.

The object of the present invention is to improve the cooling of themagnetic circuit, to improve the efficiency of the induction arrangementdescribed in the opening part of this specification and to markedlyreduce the consumption of material for the windings so that with thesame amount of power it is possible to achieve a lower weight and areduced structural size for the induction arrangement.

In accordance with the invention it is proposed that individual platepacks in the induction arrangement are displaced relative to each other.That drastically increases the surface area at both sides of the ironcore. That increase in the cooling area can be easily achieved, by afactor of between five and fifteen. Displacement of the plates of thelimbs give rise to highly effective cooling passages or ducts betweenthe core and the surrounding winding.

An increase in the induction B by about 10% also permits a number ofturns which is 10% higher. That means however that the inductanceincreases by about 121% as—see formula 1—that increases in proportion tothe square of the number of turns.

It is particularly effective if the mutually displaced plates ormutually displaced plate packs are oriented displaced through 90° withrespect to the longitudinal direction of a yoke. In that way the surfacecan be adjusted to a desired size by virtue of the displacement of theplates without in that case the winding of the adjacent magneticcircuits becoming closer.

The invention is described in greater detail hereinafter by means of anembodiment illustrated in the drawings in which:

FIG. 1 shows the principle of a magnetic choke,

FIG. 2 is a representation of the dependency of the iron losses oninduction,

FIGS. 3a and 3 b are a plan view of an induction arrangement accordingto the invention, and

FIG. 4 shows comparative views of the iron losses in dependence oninduction in the case of conventional chokes and chokes according to theinvention.

FIG. 1 shows the structure in principle of an induction arrangement bymeans of the example of a choke 1. In the illustrated example itcomprises a magnetic circuit 8, two electrical circuits 2 and, dependingon the respective situation of use involved the magnetic circuit alsohas an air gap 3. The magnetic circuit in turn comprises four elements,namely two yokes 5 and two limbs 4.

The electrical circuits 2 usually comprise a copper winding or anothermetal winding.

Depending on the area of use involved the limbs and yokes may compriselaminated dynamo plates 7 when dealing with lower and mediumfrequencies, while for higher frequencies they preferably also compriseferrite or iron powder.

As can be seen from FIG. 2 in the case of conventional inductors theiron losses P_(V,Fe) within the magnetic circuit, that is to say theiron losses of the dynamo sheets, are dependent in a relatively largerange at low frequency in quadratic relationship on the induction B.

With an even higher level of actuation (with a still greater level ofinduction) of the magnetic circuit or the dynamo plates, the iron lossesrise very steeply, and for that reason this range should be avoided asfar as possible.

In the case of chokes of conventional type the magnetic circuits are notonly formed from dynamo plates, but those dynamo plates also form acompact rectangular or square core. That core in turn is surrounded by aclosely adjoining electrical circuit, that is to say the copper winding,so that the magnetic core or the limb surrounded by the magnetic circuitare insulated from the ambient atmosphere and are therefore not in aposition of adequately removing the heat which is generated. Even if theparts of the limbs, which do not have a winding therearound, are cooledby special means, there is not an adequate possible way of removing theheat which is produced in the limbs by way of heat dissipation byradiation or heat dissipation by conduction. Thus, in spite ofconsiderable structural sizes, only relatively low levels of power losscan be removed from the limbs or the magnetic circuit.

FIG. 3 shows an induction arrangement according to the invention byreference to the example of a choke. It will be seen in this respectthat the limbs 4 surrounded by the copper winding 2 comprise a pluralityof plates 7 which are displaced relative to each other. In addition thelimb plates 7 are oriented displaced through 90° relative to thelongitudinal direction of a yoke 5 so that the displacement of the limbsrelative to each other means that the original spacing between adjacentlimbs is retained. The surface area of the limbs 4 at the sides isdrastically increased by virtue of the displacement of the plate packs 7which can be between about 2 and 10 mm in thickness. The increase insurface area and thus the cooling area by a factor of between five andfifteen can be easily achieved. As the limbs 4 are still surrounded bythe copper winding 2, that affords highly effective cooling passages orducts which, as in the case of a conventional cooling body, are capableof removing the heat which occurs in the limbs due to losses.

The highly intensive cooling of the limbs means that the induction B canbe increased without in that case the limb temperatures going intocritical ranges. An increase in the induction B by for example 10% alsopermits a 10% higher number of turns (see equation 2).

As can be seen from equation 1, the number of turns is quadraticallyinvolved in the level of the inductance L so that an increase ininduction B by 10% is equal to a rise in inductance L to 121%.

As the intensive cooling of the plates provides that they can be betterutilised, that means that at the same time the limbs can also be smallerso that their weight is reduced. A reduction in the size of the limbsalso at the same time means a reduction in the copper winding lengths,and therefore also represents a considerably lower level of consumptionof copper.

That means that the efficiency of the inductance arrangement isconsiderably improved.

It was found that, by virtue of the steps according to the invention,with the choke power remaining the same, the structural size could bereduced by between about 30 and 500% in comparison with conventionalchokes and weight could be reduced by more than 40% in comparison withconventional chokes.

FIG. 4 shows the comparison of the required amount of iron (weight) ofthe iron core of a choke. The volume of iron required Fe_(Vol)(weight)is plotted on the Y-axis. The X-axis shows the relative magneticinduction B.

The iron losses which respectively occur are constant for the curveshown. With the new cooling procedure, more losses can be removed perunit of surface area. Thus, as the curve shows, the choke can be of asubstantially smaller structure.

It is to be noted in this respect that the steps according to theinvention mean that the chokes can be acted upon by a much higher-levelof induction, in which respect iron losses per kilogram of iron stillremain markedly lower than in the case of conventional chokes. Thatmeans that the range of critical iron losses is achieved with the chokeaccording to the invention at a substantially higher level of inductionB, while the choke according to the invention is of a considerablysmaller structural size than conventional chokes.

What is claimed is:
 1. An induction arrangement, comprising: a) amagnetic circuit having a surface area and having at least two limbsconnected by at least one yoke, b) an electrical circuit having at leastone metal winding, and c) the limbs being formed by a plurality oflaminated plates each having a surface area, the laminated plates beingdisplaced relative to each other to expose at least a portion of thesurface area of more than one of the laminated plates and said laminatedplates of at least one of said limbs being oriented along planes, whichare oriented perpendicular to a plane formed by the said at least onelimb and said at least one yoke and further being oriented parallel to arotation axis of said metal winding.
 2. The induction arrangementaccording to claim 1, wherein one or more cooling passages are providedbetween at least one limb and one electrical circuit.
 3. A transformeror choke having an induction arrangement according to claim 1, whereinat least two electrical circuits are coupled together by the magneticcircuit.
 4. An induction arrangement comprising: a) a magnetic circuithaving a surface area and having at least two limbs connected by atleast one yoke, b) an electrical circuit having at least one metalwinding, and c) the limbs being formed by a plurality of plate packs oflaminated plates, the plate packs each having a surface area, the platepacks displaced relative to each other to expose at least a portion ofthe surface area of more than one of the plate packs and said laminatedplates of at least one of said being oriented along planes, which areoriented perpendicular to a plane formed by the said at least one limband said at least one yoke and further being oriented parallel to arotation axis of said metal winding.
 5. The induction arrangementaccording to claim 4, wherein one or more cooling passages are providedbetween at least one limb and one electrical circuit.
 6. A transformeror choke having an induction arrangement according to claim 4, whereinat least two electrical circuits are coupled together by the magneticcircuit.